Pachyonichya congenita (PC) is a rare genodermatosis with variable phenotypic expression affecting mainly the nails, palmoplantar skin and oral mucosa. PC clinical signs and symptoms are due to mutations of genes encoding some constitutive keratins of toenails and fingernails, skin, oral mucosa and pilosebaceous unit. On the basis of a molecular genetic analysis, the disorder is classified in two distinct subtypes: PC type I (Jadassohn-Lewandowsky syndrome) caused by mutations in the KRT16 gene encoding keratins K6a and K16, and PC type II (Jackson-Lawler syndrome) due to mutations in the KRT17 gene encoding keratin17. Keratins abnormalities result in severe onychodystrophy, acral fissured and painful hyperkeratosis, oral leukokeratosis, cystic lesions and teeth anomalies. These clinical manifestations lead to an important functional impairment and a severe decrease in quality of life.We report the cases of a 37 year-old male patient and two of his four children (a 7 year-old girl and a 3 year-old boy) with PC type I, the commonest clinical form of the disorder that manifested with thickened dystrophic toenails and fingernails, important fissured and painful plantar keratoderma, oral leukokeratosis and severe impairment of life quality. [ABSTRACT FROM AUTHOR]